Peak current control method is widely used in switching converters. In peak current control, a reference voltage and a feedback signal which indicates the output voltage of the switching converter are sent into an error amplifier to generate a compensation signal. The main transistor of the switching converter will become on once a clock signal comes, and become off when a current sensing signal indicative of the current flowing through the main transistor hits the compensation signal. Owing to the inherent delay of the control circuit, there exists a minimum on-time, wherein the main transistor can turn off only after its on-time reaches this minimum on time.
If the input voltage of the switching converter keeps increasing, the on-time of the main transistor will decrease until it reaches the minimum on-time. Hereafter, if the input voltage continues rising, the output voltage of the switching voltage will go up and a large ripple would arise accordingly.